1. Field of the Invention
This invention relates to a particle analyzing apparatus which effects beam splitting of the observation optical system and photometering optical system of a cell such as a flow cell containing particles to be examined and irradiated by an irradiating beam.
2. Related Background Art
In a prior-art particle analyzing apparatus used in a flow sightmeter, an irradiating light is applied to particles to be examined wrapped in sheath liquid and passing through a circulating portion having a minute cross-section, for example, of 200 .mu.m.times.200 .mu.m in the central portion of the flow cell, and by the resultant forward and sideways scattered light, it is possible to obtain the particulate properties such as the shape, size and refractive index of the particles to be examined. The flow sightmeter is known from U.S. Pat. Nos. 4,643,566; 4,690,561; 4,715,708 and 4,732,479, and U.S. application Ser. Nos. 106,025 and 219,816.
In the case of an example of the prior art shown in FIG. 1(A) of the accompanying drawings, the forward scattered light of particles to be examined flowing through the circulating portion 1a of a flow cell 1 by a laser light enters a photodetector 5 via a beam splitter 2 having cemented surfaces, an objective 3 and an aperture 4. A stopper 6 disposed in front of the objective 3 functions to cut the laser light (0-order light) which directly enters the photodetecter 5. In a beam observing optical system bent at 90.degree. by the beam splitter 2, an image for monitoring the beam shape and position of the irradiating laser light or detecting the stain or the like of the interior of the flow cell 1 is formed on an image sensor 8 through an imaging lens 7.
In this case, the stopper 6 is disposed rearwardly of the beam splitter 2 in order to detect the beam shape of the laser light. Thus, the direct laser light (0-order light) enters the cemented surfaces of the beam splitter 2, whereby an optical variation occurs in the adhesive agent of the cemented portion. In the interest of reducing aberrations, it is not preferable to dispose a planar beam splitter 2 having no cemented surfaces in a diverging light beam system ahead of the objective 3 because the light beam will be reflected by the front and rear surfaces of the beam splitter and the image formed by the imaging lens 7 will be a dual image.
FIG. 1(B) of the accompanying drawings, shows another example of the prior art. A planar beam splitter 2' having no cemented surfaces is disposed rearwardly of an objective 3', whereby a light beam travelling sideways is imaged on a screen 9 by a lens 7' to thereby enable the circulating portion 1a of the flow cell to be observed.
In this case, the light is intercepted by the presence of a stopper 6 disposed forwardly of the beam splitter 2' and the resolving power is reduced when the circulating portion is observed. Also, because the beam splitter 2' is disposed in the diverging light beam system, the light is reflected by the front and rear surfaces of the beam splitter 2' and the image formed by the imaging lens 7' becomes a dual image.